Johanna K. Stark

Dendrite-Free Electrodeposition and Reoxidation of Lithium-Sodium Alloy for Metal-Anode Battery

The deposition and re-oxidation of lithium metal is of interest for its potential use as the anode in lithium metal batteries. The lithium-metal anode has the highest possible theoretical capacity since only a current collector is needed to support the deposition of the metal. The density of lithium metal is 534 kg/m 3 giving it a capacity of 3862 mAh/g or 2047 mAh/cm 3 . 1 The use of lithium metal reduction/oxidation as the anode half reaction would eliminate the need for an anode structure, such as carbon or silicon, thus lowering cost, size and weight of the battery as well as the assembly complexity. However, the dendritic growth of lithium during cycling lowers the coulombic efficiency and poses safety concerns. Dendrites are needle-like structures that are formed during lithium electrodeposition. They have been found to grow on different substrates, especially at scratches or other defects on the surface. The deposition and stripping of lithium causes defects so that simply changing the substrate preparation is not an effective route to preventing dendrite growth. 2 Dendrites grow in organic as well as ionic liquid electrolytes showing that their growth is related to lithium itself rather than an electrolyte effect. The needle-like growth adds to lithium’s inefficient cycling because the dendrite can become isolated from the anode if the dendrite breaks or if the base of the dendrite is oxidized before the tip. Lithium dendrites are a severe safety concern because dendrites can short circuit the anode and cathode. Anode-cathode short circuits are especially dangerous when a flammable organic solvent is used as the electrolyte.

Platinum-Glass Composite Electrode for Fuel Cell Applications

Thin-film electrodes for a low-power direct methanol fuel cell (DMFC) were prepared by incorporating carbon-supported Pt nanoparticles (Pt/C) into a silicon dioxide glass matrix. The SiO 2 matrix was prepared via a sol-gel technique where tetraethyl orthosilicate (TEOS) was hydrolyzed by H 2 O in the presence of methanol. The Pt/C was stirred into the sol and the resulting mixture was applied to a glass membrane substrate and cured. The resulting films were ∼ 2 μm thick. Scanning electron microscopy (SEM) images indicate that the Pt/C was well dispersed, forming glass-separated conductive islands with sheet resistances in excess of 5000 Ω/□. The catalyst islands were interconnected into a conductive sheet by electrolessly depositing platinum from an aqueous plating bath. The Pt/C-SiO 2 glass composite thin-film electrodes showed high methanol oxidation peak currents of ∼ 180 mA/cm 2 when immersed in 0.5 M H 2 SO 4 , 0.5 M methanol electrolyte. The composite electrode was also applied to the anode of a 1 cm 2 passive DMFC and compared to an equivalent passive DMFC with a traditional Nafion-based Pt anode electrode with 10 M MeOH at room temperature. The composite electrode DMFC showed a 50 mV higher open-circuit voltage than the Nafion electrode cell, and the current density was also modestly improved.